Interface-Engineered Boosting of Phase Stability and Thermoelectric Performance of Ag₂Se

The development of advanced near-room-temperature thermoelectric materials is in high demand for low-grade waste heat recovery applications. In this context, silver selenide (Ag₂Se) emerged as a promising option that rivals the performance of traditional Bi₂Te₃ while being more abundant. Nevertheless, its practical exploitation is constrained by its phase instability at elevated temperatures. Here, we present a composite engineering strategy that synergistically enhances phase stability and thermoelectric performance. The integration of secondary-phase inclusions as pinning centers improves the phase stability of β-Ag₂Se and achieves a maximum figure of merit of 1.08 at 380 K, surpassing previously reported values for Ag₂Se composites. This enhanced thermoelectric performance is attributed to the combined effects of energy filtering and phonon scattering mechanisms. For practical use, the fabricated single-leg device delivers a power density of 26.6 mWcm⁻² at ΔT = 80 K. These results highlight the promise of composite engineering as a scalable, viable approach to stabilizing and improving the performance of Ag₂Se for waste-heat recovery applications. © 2026 Wiley-VCH GmbH.